I don't really 'get' what iCloud is and I've been a mac user since the green screen. I'm apparently 'over' my limit....how do I erase/trash whatever is making me be over?
You can see what your iCloud storage is used for and delete any unwanted content at settings > iCloud > Backup & Storage > Manage...... on your iOS device. Or System Preferences > iCloud > Manage...... on a Mac.